Microbial activity and population dynamics of bacteria, fungi, actinomycetes, Azotobacter and phosphate solubilizing fungi (PSF) following application of butachlor was studied in a black cotton soil. Microbial population declined significantly due to butachlor treatment. Total population of fungi showed relatively more susceptibility than bacteria to butachlor.  At recommended dose, the toxic effect of butachlor on total bacteria disappeared by 30 days after application (DAA), but the soil could not regain its lost population of Azotobacter, total fungi and PSF during the study period of 45 days. Total microbial activity in terms of CO2 evolution from the soil sharply decreased by butachlor. Addition of glucose at 10 mg/kg soil nullified the adverse effect of butachlor on total microbial activity.